Today, a secondary battery is widely used as in devices ranging from vehicles and power storage systems to small devices such as mobile phones, camcorders and notebooks.
As the secondary battery, a lithium secondary battery has an advantage of larger capacity per unit area than a nickel-manganese battery or a nickel-cadmium battery.
However, the lithium secondary battery is not suitable for a next-generation battery applicable to a vehicle because it may overheats, and its energy density is little better than about 360 Wh/kg.
Thus, there is an interest in a lithium sulfur secondary battery having a high power and a high energy density.
The lithium sulfur secondary battery refers to a battery using sulfur as a cathode active material and lithium metal as an anode. As its theoretical energy density reaches 2600 Wh/kg, it is suitable to be used as a battery for an electric vehicle requiring high power and high energy density.
In general, the lithium sulfur secondary battery uses a liquid electrolyte, which is convenient in handling. However, there are problems because a sulfide-based compound is dissolved in the liquid electrolyte and life time may become short. Further, the liquid electrolyte may leak and a fire could result at high temperatures.
Thus, there is an interest in an all-solid state lithium sulfur battery, wherein the liquid electrolyte is replaced with a solid electrolyte. The all solid-state lithium sulfur battery has advantages in its stability is high at high voltages. Further, it is easy to improve energy density per volume by simplifying the battery structure through lamination of unit cells.
However, the all solid-state battery has problems in that availability of the sulfur as a cathode active material (the amount of the sulfur used/the amount of the sulfur injected) is low, and the battery structure may become collapsed because the sulfur is lost during its reversible oxidation and reduction.
These are the problems that commonly occur in the battery using sulfur as a cathode active material. Korean Patent Publication No. 10-1384630 and Korean Patent Laid-Open Publication No. 10-2014-0001935 try to solve the problems by using a porous material as a conductive material (carbon material) of the cathode to increase the amount of the sulfur injected into the cathode.
Accordingly, the applicants reached the present disclosure as a result of continuous researching for solving the listed problems.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.